Polishing apparatus

ABSTRACT

A polishing apparatus is used for polishing a substrate such as a semiconductor wafer to a flat finish. The polishing apparatus includes a polishing tool having a polishing surface, a substrate holder configured to hold a substrate, a monitoring device configured to monitor a polishing state of the surface of the substrate being polished, and a controlling device configured to change a polishing condition on the basis of the polishing state of the surface of the substrate being polished detected by the monitoring device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polishing apparatus for polishing asubstrate such as a semiconductor wafer to a flat finish.

2. Description of the Related Art

As telecommunication means such as Internet and high-speedlarge-capacity communication network have been remarkably developed,there has been an increasing demand for miniaturization and highintegration in a semiconductor integrated circuit technology whichsupports the telecommunication means.

However, as a semiconductor device has become smaller in size and morehighly integrated, an electric signal delay in the semiconductor device,i.e., RC delay has become a large problem. The RC delay is determined bythe product of interconnect resistance R and interconnect capacitance C.Therefore, a countermeasure for preventing such RC delay is to use acombination of an interconnect metal having a low electric resistanceand an interlayer dielectric/intermetal dielectric having a lowdielectric constant.

Accordingly, instead of using tungsten (W), aluminum (Al), or aluminumalloys as a material for interconnects, there is a growing movementtowards using copper (Cu) or copper alloys which have a lower electricresistance. Further, instead of Sio₂, a low dielectric constant (i.e.,low-k) material has been developed as a material for the interlayerdielectric/intermetal dielectric. In addition to the development of thelow dielectric constant material, attempts have been made to lower adensity of the film by introducing a porous structure into the materialso that the dielectric constant of the interlayer dielectric/intermetaldielectric is further lowered.

Further, as a semiconductor device has become smaller in size and morehighly integrated, structures of semiconductor elements have become morecomplicated. In addition, the number of layers in multilayerinterconnects has been increased. Accordingly, irregularities on asurface of a semiconductor device become increased, and hence stepheights on the surface of the semiconductor device tend to be larger.This is because, in a manufacturing process of a semiconductor device, athin film is formed on a semiconductor device, then micromachiningprocesses, such as patterning or forming holes, are performed on thesemiconductor device, and these processes are repeated many times toform subsequent thin films on the semiconductor device.

When the number of irregularities on a surface of a semiconductor deviceis increased, a thickness of a thin film formed on a portion having astep tends to be small. Further, an open circuit is caused bydisconnection of interconnects, or a short circuit is caused byinsufficient insulation between interconnect layers. As a result, goodproducts cannot be obtained, and the yield tends to be reduced.Furthermore, even if a semiconductor device initially works normally,reliability of the semiconductor device is lowered after a long-termuse. At the time of exposure in a lithography process, if a surface tobe irradiated has irregularities, then a lens unit in an exposure systemcannot focus on such irregularities. Therefore, if the irregularities ofthe surface of the semiconductor device are increased, then it becomesdifficult to form a fine pattern on the semiconductor device.

Accordingly, in a manufacturing process of a semiconductor device, itbecomes increasingly important to planarize a surface of a semiconductordevice. The most important one of the planarizing technologies is CMP(Chemical Mechanical Polishing). The chemical mechanical polishing isperformed with use of a polishing apparatus. Specifically, a substratesuch as a semiconductor wafer is brought into sliding contact with apolishing surface such as a polishing pad while a polishing liquidcontaining abrasive particles such as silica (SiO₂) is supplied onto thepolishing surface, so that the substrate is polished.

This type of polishing apparatus comprises a polishing table having apolishing surface constituted by a polishing pad or a fixed abrasive,and a substrate holder, called a top ring or a carrier head, for holdinga substrate such as a semiconductor wafer. A substrate such as asemiconductor wafer is polished by the polishing apparatus in thefollowing manner: The substrate is held by the substrate holder and thenpressed against the polishing surface under a predetermined pressure. Atthis time, the polishing table and the substrate holder are movedrelative to each other for thereby bringing the substrate into slidingcontact with the polishing surface. Accordingly, the surface of thesubstrate is polished under a predetermined polishing pressure.

Generally, a low dielectric constant material has a low film adhesionstrength. Therefore, in a case where the low dielectric constantmaterial is used for the interlayer dielectric/intermetal dielectric,the following problems may arise in a polishing process:

-   -   (1) Separation (peeling-off) occurs at an interface between the        interlayer dielectric/intermetal dielectric and a metal film or        other films, resulting in failure of a fabrication process of a        semiconductor device.    -   (2) In order to prevent such separation of the interlayer        dielectric/intermetal dielectric, an excessively low polishing        pressure is required in the polishing process, thus increasing a        process time in a polishing process.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above drawbacks. Itis therefore an object of the present invention to provide a polishingapparatus which can prevent a film formed on a substrate from beingseparated during a polishing process and can eliminate a need forselecting a process condition which may increase a process time in apolishing process.

In order to achieve the above object, according to the presentinvention, there is provided a polishing apparatus for polishing asubstrate, comprising; a polishing tool having a polishing surface; asubstrate holder configured to hold a substrate, the substrate held bythe substrate holder being brought into sliding contact with thepolishing surface; a monitoring device configured to monitor a polishingstate of the surface of the substrate being polished; and a controllingdevice configured to change a polishing condition on the basis of thepolishing state of the surface of the substrate being polished detectedby the monitoring device.

According to the present invention, during polishing of the substrate,the polishing state of the surface of the substrate being polished ismonitored by the monitoring device, and the polishing condition can bechanged on the basis of the polishing state of the surface beingpolished which has been detected by the monitoring device. Therefore,even if a film composed of a material having a weak adhesion such as alow dielectric constant material is formed on the substrate, thepolishing condition is changed by detecting the polishing state having apossibility of peeling-off of the film during polishing of thesubstrate, thus preventing the film from being peeled off.

According to one aspect of the present invention, the controlling devicechanges the polishing condition when the polishing state of the surfaceof the substrate being polished detected by the monitoring devicebecomes a preset condition related to peeling-off of a film formed onthe substrate.

According to the present invention, as a preset condition related topeeling-off of a film, for example, a threshold value of a frictionalforce acting on the polishing interface is set, and when the frictionalforce which is being monitored during the polishing process exceeds thethreshold value, operational commands are sent from the monitoringdevice to the controlling device, and then the process condition iscontrolled so that the frictional force is lowered by the controllingdevice. Thus, the film formed on the substrate can be prevented frombeing peeled off. Further, since the threshold value at whichpeeling-off of the film does not occur is determined in advance, andpolishing of the substrate can be performed in such a condition that thefrictional force approaches the threshold value as close as possible,the excessively safe process which takes long time to polish thesubstrate in order to prevent the film from being peeled off is notrequired to be selected.

According to one aspect of the present invention, the film comprises alow-k film.

According to one aspect of the present invention, the monitoring devicemonitors at least one of a load torque of a motor for rotating thepolishing tool and a load torque of motor for rotating the substrateholder.

According to one aspect of the present invention, the monitoring devicemonitors a force acting on the substrate holder in a sliding directionof the substrate holder.

According to one aspect of the present invention, the monitoring devicemonitors the state of the surface of the substrate being polishedoptically.

According to one aspect of the present invention, the monitoring devicemonitors whether acoustic emission is generated or not.

According to one aspect of the present invention, the polishingcondition is a polishing load.

According to one aspect of the present invention, the polishingcondition is at least one of a rotational speed of the polishing tooland a rotational speed of the substrate holder.

According to one aspect of the present invention, the polishingcondition is a swing speed of the substrate holder.

According to one aspect of the present invention, the polishingcondition is a supply amount of a polishing liquid supplied to thepolishing surface.

According to one aspect of the present invention, the polishingcondition is a type of polishing liquid.

According to one aspect of the present invention, the polishingcondition is in-situ dressing condition.

According to one aspect of the present invention, the polishingcondition is a temperature of a polishing liquid supplied to thepolishing surface.

According to one aspect of the present invention, the polishingcondition is a temperature of the polishing surface.

According to the present invention, even if a material having a weakadhesion such as a low dielectric constant material is used for a filmof a semiconductor device, the film formed on the substrate can beprevented from being peeled off during polishing of the substrate.Further, it is not necessary to select the excessively safe processwhich takes long time to polish the substrate in order to prevent thefilm from being peeled off. Thus, the process margin can be broadened.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an overall structure of a polishingapparatus according to an embodiment of the present invention;

FIG. 2 is a schematic view showing the polishing apparatus shown in FIG.1, various sensors provided in the polishing apparatus, and apolishing-state monitoring and controlling apparatus;

FIG. 3 is a graph showing the pre-obtained data regarding therelationship between a load torque of a motor and a frictional forceacting on a polishing interface;

FIG. 4 is a graph showing the pre-obtained data regarding therelationship between reflectivity of light and a surface of a substratebeing polished;

FIG. 5 is a graph showing the relationship between a supply amount of apolishing liquid and a frictional force; and

FIG. 6 is a graph showing the relationship between types of polishingliquid and frictional coefficients.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A polishing apparatus according to embodiments of the present inventionwill be described below with reference to drawings.

FIG. 1 is a schematic view showing an overall structure of a polishingapparatus according to an embodiment of the present invention. As shownin FIG. 1, the polishing apparatus according to the present inventioncomprises a polishing table 1 having a polishing surface, a substrateholder 5 for holding a substrate 4 such as a semiconductor wafer to bepolished and pressing the substrate 4 against the polishing surface ofthe polishing table 1, and a dresser 25 for dressing the polishingsurface of the polishing table 1. The substrate 4 to be polished has alower surface comprising a low-k film which is an object to be polished.A material for forming the low-k film includes SiOC, F doped SiO₂, HSQ,MSQ, BCB (Benzo Cyclo Butene), PAE (Poly Arylene Ethers), SiO₂, SiOF,Polyimide, PSI (Polyimide siloxane), CVD-PI (CVD polyimide), PTFE(Polytetrafluoroethylene), PNT (Polynaphthalene), BCB (Benzo cyclobutane), a-C:F (fluorinated amorphous carbon), Palylene-N, Palylene-F,SOG-Siloxan, or a porous structural member made of one of thesematerials.

The polishing table 1 has an upper surface to which a polishing pad 2 isattached, and the upper surface of the polishing pad 2 constitutes thepolishing surface. The polishing table 1 is rotatable by a polishingtable drive motor 9. A polishing liquid supply nozzle 8 is providedabove the polishing table 1, and a polishing liquid Q (slurry) issupplied onto the polishing pad 2 on the polishing table 1 from thepolishing liquid supply nozzle 8.

Various types of polishing pads are available on the market. Forexample, some of these are SUBA800, IC-1000, and IC-1000/SUBA400(two-layer cloth) manufactured by Rodel, Inc., and Surfin xxx-5 andSurfin 000 manufactured by Fujimi Inc. SUBA800, Surfin xxx-5, and Surfin000 are non-woven fabrics bound by urethane resin, and IC-1000 is madeof rigid foam polyurethane (single-layer). Foam polyurethane is porousand has a large number of fine recesses or holes formed in its surface.

Although the polishing pad serves as the polishing surface, the presentinvention is not limited to the above structure. For example, thepolishing surface may be constituted by a fixed abrasive. The fixedabrasive is formed into a flat plate comprising abrasive particles fixedby a binder. With the fixed abrasive for polishing, the polishingprocess is performed by abrasive particles that are self-generated fromthe fixed abrasive. The fixed abrasive comprises abrasive particles, abinder, and pores. For example, cerium dioxide (CeO₂) or silicon oxide(SiO₂) or alumina (Al₂O₃) having an average particle diameter of 0.5 μmor less is used as an abrasive particle, and thermosetting resin such asepoxy resin or phenol resin or thermoplastic resin such as MBS resin orABS resin is used as a binder. Such a fixed abrasive forms a harderpolishing surface. The fixed abrasive includes not only the aboveplate-like fixed abrasive but also a fixed abrasive pad having atwo-layer structure formed by a thin layer of a fixed abrasive and anelastic polishing pad attached to a lower surface of the thin layer ofthe fixed abrasive.

The above polishing table and the polishing pad constitute a polishingtool. Further, the above polishing table and the fixed abrasiveconstitute a polishing tool. Here, the polishing table comprises SuS(metal), Al₂O₂, SiC, or the like.

The substrate holder 5 comprises a holder body 6 for holding the uppersurface of the substrate, and an annular retainer ring 7 fixed to thelower end of the holder body 6 for retaining an outer circumferentialedge of the substrate. The holder body 6 is made of a material havinghigh strength and rigidity, such as metal or ceramics. The retainer ring7 is made of highly rigid synthetic resin, ceramics, or the like. Thesubstrate holder 5 is connected to a substrate holder drive shaft 11 bya universal joint 10, and the substrate holder drive shaft 11 is coupledto a substrate holder air cylinder 13 fixed to a substrate holder head12. The substrate holder air cylinder 13 operates to move the substrateholder drive shaft 11 vertically to thereby lift and lower the substrateholder 5 as a whole and to press the substrate holder 5 against thepolishing table 1.

The substrate holder air cylinder 13 is connected to a compressed airsource 22 via a fluid passage 21 and a regulator R. The regulator R canregulate a pressure of compressed air or the like which is supplied tothe substrate holder air cylinder 13. Thus, it is possible to adjust apressing force to press the polishing pad 2 with the substrate holder 5,and hence a polishing pressure applied to the substrate can be adjustedto a desired value.

The substrate holder drive shaft 11 is connected to a rotary sleeve 15by a key (not shown). The rotary sleeve 15 has a timing pulley 16fixedly disposed at a peripheral portion thereof. A substrate holderdrive motor 17 is fixed to the substrate holder head 12, and the timingpulley 16 is coupled to a timing pulley 19 mounted on the substrateholder drive motor 17 via a timing belt 18. Therefore, when thesubstrate holder drive motor 17 is energized for rotation, the rotarysleeve 15 and the substrate holder drive shaft 11 are rotated in unisonwith each other via the timing pulley 19, the timing belt 18, and thetiming pulley 16 to thereby rotate the substrate holder 5. The substrateholder head 12 is supported on a substrate holder head shaft 20rotatably supported on a frame (not shown). The substrate holder head 12is swingable by rotating the substrate holder head shaft 20 so that thesubstrate holder 5 is movable between a substrate transfer position fortransferring the substrate and a polishing position on the polishingsurface of the polishing table 1. The substrate holder 5 is swingable onthe polishing surface of the polishing table 1 by rotating the substrateholder head shaft 20 in normal and reverse directions. Further, theswing speed of the substrate holder 5 is adjustable by the rotationalspeed of the substrate holder head shaft 20.

The dresser 25 comprises a diamond dresser having diamond particleselectrodeposited thereon, for example. The dresser 25 is supported froma dresser head 27 by a dresser drive shaft 26. The dresser drive shaft26 is coupled to a dresser drive motor 28, and the dresser 25 is rotatedby a dresser drive motor 28. The dresser head 27 is supported on adresser head shaft 29 rotatably supported on a frame (not shown). Thedresser head 27 is swingable by rotating the dresser head shaft 29 sothat the dresser 25 is movable between a standby position and a dressingposition on the polishing surface of the polishing table.

Overall operation of the polishing apparatus shown in FIG. 1 will bedescribed below.

In the polishing apparatus having the above structure, when thesubstrate 4 such as a semiconductor wafer is to be supplied to the topring 1, the substrate holder 5 is placed in its entirety into thesubstrate transfer position. Then, the substrate 4 is transferred to thesubstrate holder 5 by a substrate transfer apparatus (pusher) providedat the substrate transfer position, and the substrate 4 is held on thelower end surface of the substrate holder 5 under vacuum. Next, thesubstrate holder 5 holding the substrate 4 under vacuum is moved in itsentirety to a position above the polishing table 1. The outercircumferential edge of the substrate 4 is retained by the retainer ring7 so that the substrate 4 will not be dislodged from the substrateholder 5.

Then, the attraction of the substrate 4 is released. At the same time,the substrate holder air cylinder 13 connected to the substrate holderdrive shaft 11 is operated to press the substrate 4 held by the lowerend surface of the substrate holder 5 against the polishing pad 2 of thepolishing table 1. At this time, the polishing table 1 and the substrateholder 5 are being rotated by the polishing table drive motor 9 and thesubstrate holder drive motor 17 at respective desired rotational speeds.The polishing liquid Q which has been supplied from the polishing liquidsupply nozzle 8 is retained on the polishing pad 2. The substrate 4 isnow polished with the polishing liquid Q being present between thesurface (lower surface) of the substrate 4 and the polishing pad 2. Byregulating a pressure of air supplied to the substrate holder aircylinder 13, a polishing pressure applied to the substrate can beadjusted to a desired value. During polishing of the substrate 4, apolishing state of the surface of the substrate 4 being polished ismonitored, and is controlled. At the same time that the substrate ispolished, the dresser 25 is rotated at a predetermined rotational speedwhile the dresser 25 is pressed against the polishing pad 2 and thedressing liquid is supplied to the polishing pad 2. Thus, in-situdressing of the polishing pad 2 is performed.

Next, a polishing state monitoring and controlling apparatus formonitoring a polishing state of the substrate and controlling thepolishing state of the substrate during a polishing process will bedescribed with reference to FIGS. 2 through 6.

FIG. 2 is a schematic view showing the polishing apparatus shown in FIG.1, various sensors provided in the polishing apparatus, and a polishingstate monitoring and controlling apparatus. As shown in FIG. 2, thepolishing apparatus has a polishing state monitoring and controllingapparatus 30, and the polishing state monitoring and controllingapparatus 30 comprises a polishing state monitoring unit 31 and apolishing state controlling unit 32. The polishing state monitoring unit31 constitutes a monitoring device configured to monitor a polishingstate of the surface of the substrate being polished, and the polishingstate controlling unit 32 constitutes a controlling device configured tochange a polishing condition on the basis of the polishing state of thesurface of the substrate being polished detected by the monitoringdevice (described later). A motor torque of the polishing table drivemotor 9 for rotating the polishing table 1 is detected on the basis of amotor current value, and the detected motor torque is inputted into thepolishing state monitoring unit 31 of the polishing state monitoring andcontrolling apparatus 30. A motor torque of the substrate holder drivemotor 17 for rotating the substrate holder 5 is detected on the basis ofa motor current value, and the detected motor torque is inputted intothe polishing state monitoring unit 31 of the polishing state monitoringand controlling apparatus 30.

A force sensor 33 for detecting an acting force is provided on thesubstrate holder 5, and a force acting on the substrate holder 5 in thesliding direction of the substrate holder 5 is detected by the forcesensor 33. Then, the detected acting force is inputted into thepolishing state monitoring unit 31 of the polishing state monitoring andcontrolling apparatus 30. Further, an acoustic emission sensor (AEsensor) 35 is provided on the substrate holder 5, and elastic wave(described later on) detected by the acoustic emission sensor 35 isinputted into the polishing state monitoring unit 31 of the polishingstate monitoring and controlling apparatus 30.

On the other hand, an optical sensor 34 is provided in the polishingtable 1, and reflected light from the substrate 4 detected by theoptical sensor 34 is inputted into the polishing state monitoring unit31 of the polishing state monitoring and controlling apparatus 30. Theoptical sensor 34 comprises a light-emitting element and alight-receiving element. Light for measurement from the light-emittingelement is applied to the substrate 4, and reflected light from thesubstrate 4 is received by the light-receiving element. This receivedreflected light is inputted into the polishing state monitoring unit 31,as described above.

Next, operation of the various sensors and the polishing statemonitoring and controlling apparatus constructed as shown in FIG. 2 willbe described below.

The respective torque values of the polishing table drive motor 9 andthe substrate holder drive motor 17 are inputted into the polishingstate monitoring unit 31 of the polishing state monitoring andcontrolling apparatus 30. In the polishing state monitoring unit 31, africtional force acting between the surface of the substrate 4 and thepolishing surface of the polishing pad 2 on the polishing table 1 isdetected from the torque of the polishing table drive motor 9 and/or thetorque of the substrate holder drive motor 17. In this case, therelationship between the frictional force acting on the polishinginterface between the surface of the substrate 4 and the polishingsurface of the polishing pad 2 on the polishing table 1, and the loadtorque (torque of the motor) are determined in advance.

FIG. 3 is a graph showing the pre-obtained data regarding therelationship between a load torque of a motor and a frictional forceacting on a polishing interface. In FIG. 3, the horizontal axisrepresents a load torque of the motor, and the vertical axis representsa frictional force acting on the polishing interface. As shown in FIG.3, there is linear correlation between the load torque of the motor andthe frictional force.

As shown in FIG. 3, the frictional force acting between the surface ofthe substrate 4 being polished and the polishing surface of thepolishing pad 2 on the polishing table 1 is detected from a torque ofthe polishing table drive motor 9 and/or a torque of the substrateholder drive motor 17 on the basis of the pre-obtained data regardingthe relationship between the load torque of the motor and the frictionalforce acting on the polishing interface. In this manner, the detectedfrictional force acting on the polishing interface between the surfaceof the substrate 4 being polished and the polishing surface of thepolishing pad 2 on the polishing table 1 is monitored at all timesduring a polishing process by the polishing state monitoring unit 31.

The force sensor 33 provided on the substrate holder 5 comprises anacceleration sensor, and the frictional force acting on the polishinginterface between the surface of the substrate 4 being polished and thepolishing surface of the polishing pad 2 can be detected on the basis ofan acceleration (vibration) detected by the force sensor 33. In thiscase, in the polishing state monitoring unit 31, frequency componentshaving a strong correlation with the polishing process are extractedfrom signals inputted from the force sensor 33 into the polishing statemonitoring unit 31 of the polishing state monitoring and controllingapparatus 30, and the time variation of the extracted frequencycomponents is monitored. The relationship between a vibration strengthand a frictional force acting on the polishing interface between thesurface of the substrate 4 being polished and the polishing surface ofthe polishing pad 2 is determined in advance.

Further, in the optical sensor 34, visible light is applied to thesurface of the substrate 4 being polished by the light-emitting element,and reflected light from the surface of the substrate 4 being polishedis received by the light-receiving element. Then, the reflected light isinputted into the polishing state monitoring unit 31 of the polishingstate monitoring and controlling apparatus 30, and reflectivity of lightcan be detected. In the polishing state monitoring unit 31, during thepolishing process, the state of the surface of the substrate 4 beingpolished can be optically monitored by monitoring the reflectivity oflight.

FIG. 4 is a graph showing the pre-obtained data regarding therelationship between reflectivity of light and a surface of a substratebeing polished. In FIG. 4, the horizontal axis represents time(seconds), and the vertical axis represents reflectivity of light (%) ofa surface of a substrate being polished. As shown in FIG. 4, thereflectivity (%) varies rapidly after a lapse of about 30 seconds, andthereafter the reflectivity is rapidly lowered. In this case, this isbecause peeling-off of a film occurs after a lapse of about 30 seconds.By monitoring the reflectivity of light of the surface of the substrate4 being polished, generation of peeling-off of the film formed on thesubstrate 4 can be detected.

When the film of the surface of the substrate 4 being polished is peeledoff, elastic wave in an ultrasonic band is emitted, and this phenomenonis called acoustic emission. Therefore, the acoustic emission sensor 35provided on the substrate holder 5 detects this elastic wave to detectpeeling-off of the film. In the polishing state monitoring unit 31,during the polishing process, whether the acoustic emission (AE) isgenerated or not is monitored, whereby peeling-off of the film generatedin the surface of the substrate 4 being polished is monitored.

In this manner, various values including the torque of the motor, thevibration strength, the reflectivity of light, the AE, and the like aremonitored at all times during the polishing process in the polishingstate monitoring unit 31 of the polishing state monitoring andcontrolling apparatus 30. In this case, in the polishing statemonitoring unit 31, measured values such as torques, vibration strength,reflectivity of light, and the like are compared with predeterminedthreshold values at all times during the polishing process.

The above threshold values are determined in the following procedure,for example.

-   (1) A critical frictional force at which peeling-off of a film of a    substrate to be polished occurs is determined in advance.-   (2) A threshold value of the frictional force which can be applied    to the substrate during the polishing process is determined in    consideration of safety factor.

The above determined threshold value is used, and when the frictionalforce of the polishing interface which is being monitored exceeds thedetermined threshold value, operational commands are sent from thepolishing state monitoring unit 31 to the polishing state controllingunit 32, and the process condition is controlled so that the frictionalforce is lowered by the polishing state controlling unit 32.Specifically, the polishing load is lowered, the flow rate of thepolishing liquid (slurry) is reduced, the rotational speed of thesubstrate holder 5 and/or the polishing table 1 is lowered, the type ofpolishing liquid (slurry) is changed, or other controls may beperformed.

As described above, when the measured value which is being monitoredexceeds the threshold value, the operational commands are sent form thepolishing state monitoring unit 31 to the polishing state controllingunit 32. Then, as shown in FIG. 2, control of the polishing load,control of the rotational speed of the polishing table 1 and/or thesubstrate holder 5, control of the supply amount of the polishingliquid, control of the in-situ dressing condition, control of thetemperature of the polishing liquid, control of the temperature of thepolishing surface, and change of the type of polishing liquid areperformed. In this case, of these kinds of control, one or more kinds ofcontrol are suitably combined to prevent the film formed on thesubstrate 4 from being peeled off. The control of the temperature of thepolishing liquid is performed by a temperature adjustment device such asa heater or a chiller for heating or cooling the polishing liquid.Further, a control method of controlling the temperature of thepolishing surface includes a method of allowing a temperature regulatingfluid to flow from the backside surface of the polishing table, a methodof warming the polishing surface by applying light to the polishingsurface, and a method of cooling the polishing surface by ventilation.

FIG. 5 is a graph showing the relationship between a supply amount of apolishing liquid and a frictional force, and the horizontal axisrepresent a flow rate of the polishing liquid (ml/min) and the verticalaxis represents a frictional force of a polishing interface (N).

As shown in FIG. 5, the frictional force of the polishing interface canbe lowered by reducing the supply amount of the polishing liquid.Therefore, when the frictional force which is being monitored exceeds athreshold value, the frictional force is lowered by reducing the supplyamount of the polishing liquid. Thus, the film formed on the substrate 4can be prevented from being peeled off.

FIG. 6 is a graph showing the relationship between types of polishingliquid and frictional coefficients, and the horizontal axis representstypes of polishing liquid and the vertical axis represents frictionalcoefficients. In FIG. 6, Ox-1 is silicon-dioxide-film polishing slurrySS-25 manufactured by Cabot Corporation, Cu-1 is copper-film polishingslurry PL7101 manufactured by Fujimi Incorporated, Cu-2 is copper-filmpolishing slurry CMS7303/7304 manufactured by JSR Corporation, Cu-3 iscopper-film polishing slurry PL7102/DCM-G2 manufactured by FujimiIncorporated, Cu-4 is abrasive particle-free copper-film polishingslurry l, and Cu-5 is abrasive particle-free copper-film polishingslurry 2. Further, Ta-1 is barrier-metal polishing slurry B-12manufactured by Fujimi Incorporated, and Ta-2 is barrier-metal polishingslurry CMS8301 manufactured by JSR Corporation.

As is apparent from FIG. 6, the frictional force of the polishinginterface can be lowered by changing the type of polishing liquid.Therefore, when the frictional force of the polishing interface which isbeing monitored exceeds the threshold value, the frictional force islowered by changing the type of polishing liquid. Thus, the film formedon the substrate 4 can be prevented from being peeled off.

A plurality of threshold values can be determined, and the optimumprocess can be maintained by determining a lower limit and an upperlimit of the threshold values. The optimum process condition means thatthe frictional force of the polishing interface is as small as possibleand the polishing rate is as large as possible. However, it is necessaryto consider within wafer non-uniformity of the surface of the substrateto be polished or the pattern characteristics. Basically, the larger thefrictional force is, the higher the polishing rate is. Therefore, theoptimum process condition may be such a condition that the frictionalforce approaches the above threshold value as close as possible.Specifically, while the frictional force of the polishing interface ismonitored by the polishing state monitoring unit 31, if the frictionalforce is lowered excessively, then the polishing apparatus is operatedsuch that parameters are controlled so as to increase the frictionalforce.

Although certain preferred embodiments of the present invention havebeen shown and described in detail, it should be understood that variouschanges and modifications may be made therein without departing from thescope of the appended claims.

1. A polishing apparatus for polishing a substrate, comprising; apolishing tool having a polishing surface; a substrate holder configuredto hold a substrate, the substrate held by said substrate holder beingbrought into sliding contact with said polishing surface; a monitoringdevice configured to monitor a polishing state of the surface of thesubstrate being polished; and a controlling device configured to changea polishing condition on the basis of said polishing state of thesurface of the substrate being polished detected by said monitoringdevice.
 2. A polishing apparatus according to claim 1, wherein saidcontrolling device changes said polishing condition when said polishingstate of the surface of the substrate being polished detected by saidmonitoring device becomes a preset condition related to peeling-off of afilm formed on the substrate.
 3. A polishing apparatus according toclaim 2, wherein said film comprises a low-k film.
 4. A polishingapparatus according to claim 1, wherein said monitoring device monitorsat least one of a load torque of a motor for rotating said polishingtool and a load torque of motor for rotating said substrate holder.
 5. Apolishing apparatus according to claim 1, wherein said monitoring devicemonitors a force acting on said substrate holder in a sliding directionof said substrate holder.
 6. A polishing apparatus according to claim 1,wherein said monitoring device monitors the state of the surface of thesubstrate being polished optically.
 7. A polishing apparatus accordingto claim 1, wherein said monitoring device monitors whether acousticemission is generated or not.
 8. A polishing apparatus according toclaim 1, wherein said polishing condition is a polishing load.
 9. Apolishing apparatus according to claim 1, wherein said polishingcondition is at least one of a rotational speed of said polishing tooland a rotational speed of said substrate holder.
 10. A polishingapparatus according to claim 1, wherein said polishing condition is aswing speed of said substrate holder.
 11. A polishing apparatusaccording to claim 1, wherein said polishing condition is a supplyamount of a polishing liquid supplied to said polishing surface.
 12. Apolishing apparatus according to claim 1, wherein said polishingcondition is a type of polishing liquid.
 13. A polishing apparatusaccording to claim 1, wherein said polishing condition is in-situdressing condition.
 14. A polishing apparatus according to claim 1,wherein said polishing condition is a temperature of a polishing liquidsupplied to said polishing surface.
 15. A polishing apparatus accordingto claim 1, wherein said polishing condition is a temperature of saidpolishing surface.